(1) Field of the Invention
The present invention relates generally to underwater transducers. More particularly, this invention relates to a transducer having an in-line screw exerting compressive force to prevent generation of excessive tensile stress.
(2) Description of the Prior Art
Acoustic signals are commonly used for underwater navigation, communications, and imaging. The devices that generate underwater sound for these applications convert input energy into mechanical vibrations. These vibrations are then radiated into the surrounding medium. This conversion of energy from one form to another is termed transduction, and the devices that make this conversion are called transducers.
Many of the transducers now in use contain electromechanical ceramic materials. These ceramics deform when electric or magnetic fields are applied to them. The deformations produce the mechanical vibrations that are radiated by the transducers as underwater sound. However, if excessive tensile stresses are allowed to develop in the ceramics as they deform, the ceramics will fracture, and the transducers will cease to operate property, or may fail completely. To prevent this problem a permanent compressive stress must be applied to the ceramics.
Prior art designs have created compressive bias stress using stress rods. One such example of the prior art is shown in U.S. Pat. No. 2,930,912 to H. B. Miller. Miller uses multiple stress rods alongside his stack of ferroelectric elements; however, this increases the complexity of the design, and stress rods become particularly difficult to implement with small drivers. Miller also uses a central stress rod to exert compressive force. Typically, an axial hole extends throughout the entire length of the ceramic driver to accommodate the stress rod. Since the hole occupies a volume that could otherwise be filled by additional driver material, performance of the transducer may be decreased by this design. Furthermore, machining such holes in small drivers having, for example, outer diameters of about 2 mm is difficult to accomplish. In FIG. 6 Miller shows a pair of annular retainer members that engage the threaded housing to compress the ferroelectric stack. However, it appears that Miller compresses his ferroelectric stack between essentially identical threaded retainer caps and does not compress his ferroelectric stack between a radiating diaphragm and an adjustable screw within a housing. Furthermore, during tightening of the end members, torsional loading might be transmitted to the stack and damage it.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for an electroacoustic transducer having a driver element electrically coupled to conductive components and a coil spring disposed in-line with a radiating diaphragm and a threaded member that hold the driver in compression without transmitting torsional loads.
Accordingly, it is an object of the invention is to provide an improvement for electroacoustic transducers.
Another object of the invention is to provide an apparatus for compressing the driver element of an electroacoustic transducer that eliminates one or more stress rods otherwise used to maintain compressive bias in conventional transducers.
Another object of the invention is to provide an electroacoustic transducer compressively biasing a driver with an in-line screw member.
Another object of the invention is to provide an electroacoustic transducer having minimum parts to compress a ferroelectric driver and couple electrical signals thereto.
Another object of the invention is to provide an electroacoustic transducer having uncomplicated disassembly and reassembly when replacing a driver element.
Another object of the invention is to provide an electroacoustic transducer having its driver element in a conductive holder engaging channels to prevent creation of torsional stresses in the driver element as a screw member creates compressive stress in the driver element.
Another object of the invention is to provide an electroacoustic transducer having one end of its driver element coupled to a hemisphere which has its apex contacting the center point of an axially aligned diaphragm to distribute loads and reduce the possibility of creating uneven stresses in the driver element that may otherwise fracture it.
Another object of the invention is to provide an acoustic transducer having an end of its driver element coupled to a resilient coil spring to make electrical contact with the driver element via a conductive holder and screw member that exert compressive bias.
Another object of the invention is to provide an acoustic transducer having a diaphragm for radiating acoustic energy that also functions as part of the electrically conductive path for the driver.
These and other objects of the invention will become more readily apparent from the ensuing specification when taken in conjunction with the appended claims.
The present invention provides an electroacoustic transducer that has a driver element coupled to an axially disposed diaphragm. A coil spring conducts electrical power to the driver element through an axially in-line conductive screw member, holder, and mounting plug that exert compressive bias but no torsional loads on the driver element to prevent development of excessive tensile stress during projection of acoustic signals.